Abstract: Reversibly gelling aqueous and oil emulsions are disclosed which can be modified to incorporate oil soluble pharmaceutical compounds for delivery to physiological systems in a soluble form and which undergo significant changes in viscosity in response to substantially simultaneous changes in both temperature and pH. The compositions are formed of relatively low concentrations of a stable combination of at least one pH-sensitive reversibly gelling polymer, at least one temperature-sensitive reversibly gelling polymer and at least one organic oil. The compositions can be formulated to exhibit a sol-gel transition over a wide range of conditions and viscosities and may be modified to incorporate a pharmaceutical compound for utilization as droppable or injectable drug delivery systems which will gel following administration to a physiological system for the sustained delivery of such pharmaceutical compounds.